Human factors, EVA & space medicine
A crewed mission does not simply add passengers to a robotic vehicle. The human body imposes atmosphere, temperature, sleep, food, exercise, radiation protection and medical care. Crew also adds extraordinary diagnostic and improvisational capability, but that capability declines with fatigue, stress, illness or poor interfaces. Human systems engineering therefore seeks robust performance rather than assuming heroic, infallible people.
Mastery objectives
- explain concepts with units and assumptions
- redo a simple calculation by hand before using a tool
- identify at least one failure mode or model limitation
- connect the discipline to a complete Mars architecture
1. Human performance and physiological limits
Performance varies with sleep, circadian rhythm, workload, stress, nutrition and health. A procedure designed for a rested operator may become dangerous after a long overnight anomaly. Systems should reduce reliance on memory, provide clear cues and preserve recovery time. Fatigue is a system risk, not a moral failure of the crew.
Engineering habit. For “human performance and physiological limits”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
Approfondissement — Human performance: fatigue is a system variable
A tired crew does not suddenly lose all skill. People become slower, omit more steps and handle simultaneous signals less reliably. That makes fatigue dangerous because degradation can remain subtle until a bad moment. Workload can be tracked through task duration, interruptions, procedure complexity and sleep quality, but no single metric replaces observed performance.
On Mars, schedules should be designed as resource budgets. A six-hour EVA does not consume only six hours: preparation, suit donning, depressurization, egress, return, repressurization, suit maintenance and debrief all use time and attention. If an emergency occurs immediately afterward, the system must assume a crew that is already depleted. Human margin should therefore be protected like electrical or thermal margin, not routinely consumed during nominal operations.
2. Human factors and interface design
An alarm must be perceivable, understandable and prioritized. Too many simultaneous alarms become noise; critical information hidden on a secondary display delays diagnosis. Design considers anthropometry, gloves, visibility, lighting, maintenance access and procedural compatibility. The interface is part of the safety system.
Engineering habit. For “human factors and interface design”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
3. Space medicine and increasing autonomy
Far from Earth, a crew cannot assume rapid evacuation. Diagnostic capability, medicines, emergency procedures, telemedicine, consumables and cross-trained skills must be defined. Required autonomy depends on communication delay and return time. A durable settlement needs more than a first-aid kit; it needs a healthcare chain.
Engineering habit. For “space medicine and increasing autonomy”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
Approfondissement — Operational medicine: making decisions when evacuation is not available
On Earth, a medical team can stabilize a patient and transfer them to a higher level of care. On Mars, the higher level may not exist. Medical design has to begin with actual capability: diagnostics, drugs, imaging, limited surgery, dentistry, rehabilitation and isolation. Treatment decisions also interact with the remaining stock and risk to the rest of the crew.
Triage changes when rapid evacuation is impossible. A serious EVA injury may require two rescuers, interrupt critical work and consume irreplaceable medical supplies. Procedures therefore have to connect medicine, operations, resources and command. Prevention remains the strongest control: ergonomic design, training, load limits, fall protection, fatigue monitoring and authority to stop work before schedule pressure turns an avoidable incident into a medical emergency.
4. EVA: turn a human into a mobile autonomous system
Extravehicular activity combines a pressurized suit, oxygen, CO₂ removal, thermal control, communications, power, mobility and procedures. Every minute outside consumes resources and exposes the crew to hazards. Mars adds dust, terrain, distance and airlock management. An EVA is therefore a complete mission nested inside the main mission.
Engineering habit. For “eva: turn a human into a mobile autonomous system”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
Approfondissement — EVA budget: time, oxygen, carbon dioxide removal, cooling and energy must all close
An extravehicular activity has several simultaneous budgets. Maximum duration depends on oxygen, carbon-dioxide removal, cooling, battery energy and emergency reserve. If a battery stores energy E = 3.0 kWh and average power is P = 0.42 kW, the theoretical energy-limited time is t = E ÷ P = 3.0 ÷ 0.42 ≈ 7.14 h. Here E is energy, P power and t time. That does not mean the EVA may last 7.14 h; another consumable may become limiting first.
The operational plan therefore uses the tightest constraint and keeps reserve. It must also cover a slower-than-planned return caused by injury, rover failure, an unavailable airlock or low visibility. Emergency reserve is not part of the nominal work budget. A base that repeatedly spends its EVA oxygen reserve to gain thirty minutes of productivity has already turned a survival margin into operational debt.
5. Spacesuits, airlocks and contamination
A spacesuit maintains pressure and gas composition while allowing movement. The airlock manages pressure transitions, equipment and contamination. Martian dust creates problems for seals, filters, abrasion and habitat entry. Architectures can reduce dust transfer through intermediate zones, cleaning procedures and material choices.
Engineering habit. For “spacesuits, airlocks and contamination”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
6. Robotics as a crew partner
Robots, manipulators and rovers can prepare sites, move loads or inspect areas before human exposure. The question is not ‘human or robot’ but how to allocate tasks according to strength, precision, judgement, delay and risk. A good interface lets crew supervise multiple systems without becoming the bottleneck for every operation.
Engineering habit. For “robotics as a crew partner”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
7. Nominal procedures, emergencies and abort criteria
A nominal procedure explains how to succeed; an emergency procedure must also explain when to stop. Fire, depressurization, toxicity, medical crisis or power loss need explicit priorities. Immediate actions should be simple and trained. Later actions can use checklists, diagnosis and ground support.
Engineering habit. For “nominal procedures, emergencies and abort criteria”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
8. Training, simulation and repetition
Operational skill grows through realistic repetition. Simulators, mock-ups, integrated scenarios and constrained training let crews learn from errors without losing the vehicle. Injected failures force teams to practise communication, authority and recovery. Training must cover rare transitions, not only frequent nominal operation.
Engineering habit. For “training, simulation and repetition”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
9. Team, leadership and delayed communications
A Mars crew cannot wait for Earth approval for every decision. Roles, delegation and authority limits must be prepared. Leadership can shift with the situation: a specialist may hold technical authority during a fault and return it later. Handover quality and operational logs become essential when decisions unfold over days.
Engineering habit. For “team, leadership and delayed communications”, write the inputs, outputs, units and validity range first. Then build one nominal and one degraded case. This two-case approach prevents a correct equation from being mistaken for an operationally robust Mars architecture.
Worked example step by step
The work method is always the same: state what every symbol represents, convert all units into a coherent system, perform the operation, then translate the result into a sentence. Finally perform an order-of-magnitude check. If the answer changes by a factor of one thousand because millimetres were treated as metres, the conversion must be visible in the calculation.
Progressive exercise
- Choose a simple case and list every input with units.
- Compute the nominal result without margin.
- Vary the most uncertain parameter by ±20% and compare.
- Inject one credible failure and explain which indicator detects it.
- Decide whether the system continues, degrades or stops.
Reasoned solution
A good solution is not only the final number. It shows conversions, why the equation applies, sensitivity and the resulting decision. If different plausible assumptions lead to the same operational decision, the design is relatively robust to that uncertainty. If a small variation reverses the decision, the parameter becomes a priority for measurement or margin.
Validation mini-project
Build a two-to-four-page engineering note applying this course to one Mars subsystem. Include need, assumptions, functional sketch, hand calculation, second calculation or simulation, uncertainties, injected failure, decision criteria and three primary references. The goal is a chain of evidence that another reader can reproduce.
Common errors to detect
- mixing units or frames without explicit conversion;
- presenting calculated values as measured data;
- ignoring a model’s validity range;
- confusing numerical precision with physical accuracy;
- sizing only the nominal case with no margin or degraded mode.